1. Field of the Invention
The invention relates to an apparatus for recording a digital information signal on a record carrier, the digital information signal comprising a serial datastream of information packets, the information packets comprising a packet identifier and portions of information of one or more programs, packets having the same packet identifier belonging to the same program, the apparatus comprising:
(a) input means for receiving the digital information signal, PA1 (b) signal processing means for processing the digital information signal into a recording signal suitable for recording on the record carrier, and PA1 (c) writing means for writing the recording signal on the record carrier. The invention also relates to a method for recording the digital information signal. PA1 (d) detect the presence of a clock reference signal in the packets in the serial datastream of information packets, PA1 (e) retrieve the packet identifier from the first packet in which a clock reference signal has been detected and store the packet identifier retrieved from that packet in a memory, PA1 (f) subsequently retrieve clock reference signals from those packets having a packet identifier which equals the packet identifier stored in the memory, PA1 (g) monitor the time interval since the last occurrence of a clock reference signal in/from those packets having a packet identifier which equals the packet identifier stored in the memory, and PA1 (h) return to step (d) upon the said time interval exceeding a predetermined time interval.
2. Description of the Related Art
An apparatus as defined in the opening paragraph is disclosed in International Patent Application WO 96/30.905, corresponding to U.S. Pat. No. 5,953,483, Document D1 in the List Of Related Documents that can be found at the end of this description.
The digital information signal may be in the form of an MPEG transport stream, comprising packets that may occur irregularly in the transport stream.
The ISO/IEC 13.818-1 international standard, part 1, `Systems`, Document D5 in the List Of Related Documents, includes a description of the transport stream, for transmitting a plurality of programs, for broadcasting purposes or for transmission via a cable network. Each program comprises one or more data compressed digital video signals and one or more corresponding data compressed audio signals. The transport packets in the transport stream comprise 188 bytes of information each.
Packets in the MPEG serial data stream comprise, apart from `system information`, one kind of information, that is: either a portion of a video signal, or a portion of an audio signal or a portion of a data signal. A packet comprises information of only one of the video signals, or one of the audio signals or one of the data signals transmitted via the MPEG serial data stream.
A transmission of such an MPEG information signal in the form of a recording on and a reproduction from a record carrier, requires special measures to be taken in order to realize such kind of transmission.
International Patent Application WO 96/30.905, Document D1, International Patent Application WO 95/27.978, corresponding to U.S. Pat. No. 6,008,959 (PHN 14.818), Document D3, and Internation Patent Application WO 95/27977, corresponding to U.S. Pat. No. 5,596,581 (PHA 21.886), Document D4 in the List Of Related Documents, describe various of such measures to realize a recording and reproduction of an MPEG information signal.
It can generally be said that the recording of a complete MPEG information signal is not well possible, because of the too high data-rate of the MPEG information signal, compared to the bandwidth of the recording medium. Therefore, the above Documents D1, D3 and D4 disclose the selection of one program, that is, one video signal and its corresponding audio signal(s), from the MPEG serial datastream for recording. As a consequence, generally, transport packets will be selected on an irregular basis as a function of time. In order to preserve the timing relation between the subsequent packets selected, after having recorded and reproduced the packets, the earlier filed Documents describe the measure of inserting timing information (or a `time stamp`) in each of the packets recorded. Upon reproduction, the timing relation between the subsequent packets can be regained using the time stamps.
More specifically, Document D1 disclose the generation of the time stamps in response to clock reference signals retrieved from packets in the serial datastream. These clock reference signals, defined as `program clock reference` (PCR) in the above ISO/IEC standard, Document D5, occur (generally irregularly) in the MPEG datastream, are retrieved from the datastream and compared with the count value of a counter that is clocked by a 27 MHz clock contained in the recording apparatus, so as to synchronize the counter, by controlling the clock frequency of the 27 MHz clock. The clock further clocks a second counter which generates the time stamps for combining to a corresponding packet.